1. Field of the Invention
This invention relates to a forming machine used for fully enclosed die forging etc.
2. Description of the Prior Art
Generally, a fully enclosed forming method in which a punch is inserted into at least one of a pair of dies to have the punch and the die relatively displaced, thereby deforming a material or a processing method for punching a material is being used extensively to reduce times of forming steps, produce complicated-shaped products, pierce without deforming the entire shape, and improve material yields.
For example, making a formed product 11 as shown in FIG. 12 (a) from a material 13 as shown in FIG. 12 (b) requires several steps when an ordinary swaging is applied. But, such steps can be reduced to one step by employing a forming method consisting of holding the material 13 with upper and lower dies 17, 19 and moving a punch 21 in the direction of arrow A FIG. (13).
The above step requires force to keep the upper and lower dies 17, 19 contacted or a closing force.
FIG. 14 shows a forming machine to effect the forming method of FIG. 13, in which reference numerals 17, 19 indicate upper and lower dies vertically disposed to face each other.
The upper die 17 is supported by an upper holder 25 which is fixed to an upper die set plate 23. The upper die 17 has an upper punch 27 inserted therein, which upper punch 27 has the bottom end of a knockout pin 29 contacted thereto.
The lower die 19 is supported by a ring member 33 through a ring 31. Both lower die 19 and ring member 33 having a lower punch 35 inserted therein.
Into the ring member 33 is inserted a column part 41 of a plate 39 which has its bottom end fixed to a lower die set plate 37.
The ring member 33 is disposed within a lower holder 43 which guides the ring member 33 to move vertically. This lower holder 43, the bottom end of the ring member 33 and the plate 39 form a cylinder chamber 45.
With the forming machine structured as described above, first a slide (not shown) lowers from a state illustrated in the left half of FIG. 14, the upper die 17, lower die 19 and ring member 33 lower as shown in the right half of FIG. 14, but the lower punch 35 moves relative to the lower die 19 because the lower punch 35 is fixed, and the material 13 is subjected to closed forming to produce the formed product 11.
This forming machine supplies hydraulic fluid into the cylinder chamber 45 to move the ring member 33 upward, and at the same time discharges the extra fluid outside through a relief valve 51 by the downward movement of the ring member 33, thereby providing the closing force for the upper die 17 and the lower die 19.
However, in such a conventional forming machine, the upper die 17 and the lower die 19 require the closing force much greater than required for closing, and a great slide stroke is required, thus causing a disadvantage of increasing the required workload of the press.
More specifically, to produce the formed product 11 as shown in FIG. 12 (a) for example, the closing force required at a bottom dead center becomes maximum as shown in FIG. 15, so that the closing force is required to be set based on the bottom dead center. Load P.sub.F of the lower punch 19 varies as shown by a dotted line with respect to the moving slide, and the closing force given is much greater than required until the slide reaches about the bottom dead center. And the ring member 33 needs a stroke S.sub.1 as shown in FIG. 14, requiring workload corresponding to the area of the section enclosed by slant lines as shown in FIG. 15.
As a result, a press with greater torque capacity is needed, and the energy required for forming increases.
Besides, since the upper and lower dies 17, 19 start contacting at a position much higher than the bottom dead center, automated parts have inferior approach in automated production, and a press with a long slide stroke is required.
Further, forming an excessively voluminous material may damage the dies, and the upper and lower dies 17, 19 do not contact each other, resulting in having difficulty in securing a prescribed-sized formed product 11.
A forming machine similar to the one described above is known disclosed in Japanese Patent Publication No. 56-21498. This machine is fixed to a mechanical press, and each hydraulic pressure supplying device is disposed outside of the forming machine, requiring troublesome work for replacement of dies, maintenance, etc. with inferior flexibility to be applied to make various formed products.